Molecular Modeling of Anti-Bredt Compounds

Abstract

The molecular structure and thermochemical stability of 40 bicyclic alkenes and imines containing between five and eight heavy atoms has been investigated computationally by high-level G3/B3LYP method. The same method was also used to study their building blocks: monocyclic alkenes and imines. The relative stability of isomers, standard enthalpies of formation and strain energies are discussed and compared. Our results suggest that molecular mechanics provides an unsatisfactory description of strain energies in bridgehead alkenes. Some bridgehead alkene and imine species represent structures which are not local minima on the potential energy surface and are hence unlikely to be isolated. Furthermore, some bicyclic alkenes and imines have open-shell 1,2-diradical character.

Chemistry of Bridged Lactams and Related Heterocycles

“…Bridged olefins with olefin strain energy lower than 17 kcal/mol were suggested to be isolable, those with olefin strain energy between 17 and 21 kcal/mol were classified as observable, and those with olefin strain energy higher than 21 kcal/mol were grouped as unstable . Despite the outlined above differences between bridged amides and bridged olefins, − Schleyer’s olefin strain energy provides a useful predictive tool for evaluating the stability and likelihood of isolation of bridged lactams. Figure presents structures of several of the more common ring systems of bridged lactams, the year of their first synthesis, and the corresponding bridged olefins with their olefin strain energy as calculated by Schleyer. − From comparison of these values, it is evident that even highly strained bridged lactams are stable enough for isolation (for example, compare bridged olefins 10 , 11 , and 17 with bridged lactams 18 , 19 , and 25 ).…”

Assembly of Water‐Soluble, Dynamic, Covalent Container Molecules and Their Application in the Room‐Temperature Stabilization of Protoadamantene

“…The 1 H NMR properties of the guest inside hemi‐carceplex B (vide infra) and the lack of reactivity of A and B towards oxygen rules out adamantene as the guest. Free adamantene 4 15a and encapsulated bicyclo[2.2.2]oct‐1‐ene, which has a similar olefinic strain to 4 ,14c, 32 react with atmospheric oxygen within seconds at room temperature,8a whereas ( Z )‐bicyclo[3.2.1]oct‐1‐ene, which has a trans ‐cycloheptene ring like 5 , adds oxygen only at elevated temperature 8a…”

Experimental and Computational Mechanistic Investigation of Chlorocarbene Additions to Bridgehead Carbene–Anti-Bredt Systems: Noradamantylcarbene–Adamantene and Adamantylcarbene–Homoadamantene

“…1a: λ max = 337, 344, 355 nm; 1 H NMR (300 MHz, C 6 D 6 ) δ 2.09 (t, J = 6. 4 Phenylchlorodiazirine (8). 30 To a mixture of lithium chloride (3.57 g, 84 mmol, 12 equiv) and benzamidine hydrochloride (1.09 g, 7.0 mmol, 1.0 equiv) were added 50 mL of dimethyl sulfoxide and 50 mL…”

“…Molecules with strained, distorted geometries fascinate chemists, whether from the sheer challenge of synthesizing these seemingly unfathomable (by the laws of chemistry) structures or simply the beauty of the “abnormal” . In particular, the geometries, stabilities, and reactivities of bridgehead alkenes have been a source of intrigue since Bredt proposed his rule almost a century ago. − Increasing numbers of natural products containing bridgehead alkenes have been isolated and characterized, and their total syntheses achieved . Bridgehead alkenes show diverse reactivity: carbocation rearrangements to Diels–Alder chemistry to radical trapping …”